PROJECT SUMMARY The pathogenesis of Alzheimer?s disease (AD) is characterized by the accumulation and amyloid fibril formation of amyloid-? (A?) peptides in the brain. This renewal application proposes to continue our research in the current grant period towards understanding the mechanistic roles of the dynamic and charge-rich N- terminal region of A? peptide in A? amyloidogenesis. In the new grant period, we propose to expand our systematic N-terminal mutagenesis approaches, and delve into the roles of the N-terminal residues, including those involved in mutagenesis in familial Alzheimer?s disease (FAD), in regulating the microscopic mechanisms of the rate-limiting nucleation process along the aggregation pathway. Importantly, the renewal project will be extended to elucidate the effect of the N-terminus in modulating A? oligomerization and fibrillization under the conditions that mimic the in vivo environment. Our central hypothesis is that the flexible and hydrophilic N-terminal region of A? is crucial for driving the interactions of the peptide with lipid membrane structures and polyelectrolytes that exist ubiquitously in the brain. We will identify the N-terminal key residues and critical interactions that may play dominating roles in determining A??membrane binding kinetics and thermodynamics, membrane-templated aggregation, A?-induced membrane permeabilization and disruption, and A? cellular toxicity. An unnatural amino acid p-cyanophenylalanine, which has been successfully employed to identify the local dynamics in A? aggregation in the current grant cycle, will be further applied to elucidate the residue-specific dynamics of membrane adsorption and insertion of A? peptide. The mechanistic roles of the N-terminus in mediating polyelectrolyte-regulated A? aggregation and membrane disruption will also be dissected. The outcome of the proposed research will provide novel insight into the underlying mechanistic function of the dynamic N-terminal region in modulating A? aggregation pathway, shedding light on the mechanisms of A? amyloidogenesis in vivo and the origin of A? pathology in AD. The knowledge from this research may also allow the identification of potential molecular targets, such as the N-terminal key residues and crucial interactions, for design of strategies to manipulate A? self- assembly in vivo, which could illuminate the development of new therapeutic treatment for AD.